<?php
$select = $this->selectSlideshow('show', $this->getData('show', $this->data->get));
if ($select instanceof Zend_Form_Element) {
    $select->setLabel($this->getTranslation('Select a slideshow'))
           ->setValue($this->getData('show', $this->data->get))
           ->setBelongsTo('module');
}
echo $select;